In today's radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, 3rd Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. A radio communications network comprises radio base stations providing radio coverage over at least one respective geographical area forming a cell. The cell definition may also incorporate frequency bands used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. User equipments (UE) are served in the cells by the respective radio base station and are communicating with respective radio base station. The user equipments transmit data over an air or radio interface to the radio base stations in uplink (UL) transmissions and the radio base stations transmit data over an air or radio interface to the user equipments in downlink (DL) transmissions.
One important aspect with radio communications networks also referred to as wireless networks is to ensure that the radio communications network is simple to deploy and cost efficient to operate. The vision is that the radio communications network shall be self-organizing in as many aspects as possible. Furthermore, good coverage is important when aiming at a mobile broadband experience, both outdoors and indoors. Typically, this coverage is provided via radio base stations covering larger cells, also referred to as macro base stations, with dedicated transport connections, but it is also possible to consider self-backhauling radio base stations also referred to as Relay Nodes (RN) where the same technology is used both for user data between a user equipment and the RN and for the transport connection between the RN and a radio base station with a dedicated transport connection. Self-backhauled here means that the RN is acting as a relay node to the donor radio base station.
The architecture of the 3G Long Term Evolution (LTE) system may thus include Relay Nodes (RN) also called relay base stations. Furthermore, the LTE architecture discloses logical interfaces between radio base stations (eNBs) called X2 interfaces, and between radio base station and Mobility Management Entity (MME) or Serving Gateway (S-GW), called S1 or S11 interfaces. The radio base station serving the RN acts as an X2 and S1 proxy, terminating and forwarding the X2 communication between the RN and another radio base station, and the S1 communication between the RN and the MME. The radio base station serving the RN may be referred to as a donor radio base station (DeNB).
RNs that are self-backhauling are further considered for LTE Advanced. LTE-Advanced extends LTE Release 8 with support for relaying as a tool to improve e.g. the radio coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide radio coverage in new areas.
RNs are wirelessly connected to a respective donor cell of a donor radio base station (donor eNB) via a radio interface denoted a Un interface, and user equipments are connected to respective RN via a radio interface denoted a Uu interface. The donor radio base station further connects the respective RN to the core network, e.g. the Evolved Packet Core (EPC) in LTE. The Uu interface is the radio interface between the user equipment and the RN. The Un interface is the radio interface between the RN and the donor radio base station.
The Un interface connection may be a “Type 1” connection, which means that the connection is an in-band connection, in which case the eNB-to-RN connections or links share the same frequency band with direct eNB-to-UE connections or links within the donor cell. The Un interface connection may furthermore be a “Type 2” connection, which means that the connection is an out-band connection, in which case the eNB-to-RN connection does not operate in the same band as direct eNB-to-UE connections within the donor cell.
At least “Type 1” RNs are supported by LTE-Advanced. A “Type 1” RN is an in-band RN that controls cells, each of which appears to a user equipment as a separate cell distinct from the donor cell. The cells have their own Physical Cell ID (PCI), which is a fingerprint used by a user equipment to identify the cell, and transmit their own synchronization channels and reference symbols. In the context of single-cell operation, the user equipment receives scheduling information and data transmission feedback directly from the in-band RN and sends its control information to the in-band RN. The in-band RN appears as a radio base station to a legacy user equipment, i.e. the in-band RN is backwards compatible. The in-band RN may be nomadic meaning that it may change donor eNBs over time, via disruptive events such as physical relocations or the relay node associated with the disconnection of the radio interface. The in-band RN may further be inactive at times for example to save energy.
To a large extent, the RNs may be perceived as any radio base station in the radio communications network. For example, the connections X2 and S1 between RN and other radio base stations are established, partly over Un. But also, the RN is handled to a large extent as any user equipment served by the serving radio base station. For example, when the RN is installed, it attaches to the radio communications network via the UE attach procedure, which is a procedure used to attach a user equipment to the network, and first when Radio Resource Control (RRC) connectivity is established, the serving radio base station is informed by the core network that the user equipment is in fact a RN.
From the perspective of the RN it is not possible to disclose whether a certain type of radio network connection is established between the donor radio base station and a neighboring radio base station. Since the RN may need to select between different types of radio network connections e.g. X2 connectivity and S1 connectivity, when for example performing handover, the performance of the radio communications network will be reduced if the wrong type of radio network connection is selected.